Understand Co-channel interference

[derobbacher]

Our customer is complaining about increasing disconnects of Apple devices after rollout of many of these devices.

Another external consultant found "Channel overlap issue" as a possible source of problem.

I'm wondering now how to deal with that, because we see not many problems on the WLC SW-Ver. 7.4.130.

We have put the Cisco AIR-LAP1142N WLAN APs  in a quite high density into the buildings years ago with

no problems for laptop-users these days. The SSid is provided on both bands with bandselect disabled.

Now I try to understand what interference really is out there.

I have added a screenshot and would like to know looking at the interference by Channel picture:

Can someone tell me what the blue and what the red columns are standing for ?

The interference profile states "passed" by the way.

And looking at the RX neighbor information I  would like to know:

Are the other WLAN APs in Channel1 and 11 causing the shown interference ?

And how can I drill down a channel overlap problem for Apple devices in general ?

[Leo Laohoo]

Co-channel interference from where?  Is DCA and TPC enabled and set to dynamic?

What kind of Apple devices?  iPads/iPhones/iTouch?  

[derobbacher]

Hello Leo, we have enabled DCA and TPC and the RRM has chosen mostly

TX Power Level 6 within the 2.4 GHz-Band:

      Num Of Supported Power Levels ............. 7
      Tx Power Level 1 .......................... 17 dBm
      Tx Power Level 2 .......................... 14 dBm
      Tx Power Level 3 .......................... 11 dBm
      Tx Power Level 4 .......................... 8 dBm
      Tx Power Level 5 .......................... 5 dBm
      Tx Power Level 6 .......................... 2 dBm
      Tx Power Level 7 .......................... -1 dBm
      Tx Power Configuration .................... AUTOMATIC
      Current Tx Power Level .................... 6
      Tx Power Assigned By ...................... DTPC

We have disabled also lower speeds within 2.4 GHz-Band:

Operation Rate Set
        12000 Kilo Bits.......................... MANDATORY
        18000 Kilo Bits.......................... SUPPORTED
        24000 Kilo Bits.......................... SUPPORTED
        36000 Kilo Bits.......................... SUPPORTED
        48000 Kilo Bits.......................... SUPPORTED
        54000 Kilo Bits.......................... SUPPORTED

RRM is configured with Coverage Optimal Mode (TPCv1) for 802.11b TX Power Control.

The Multifloor-building is equipped with several WLAN APs per floor and from a client perspective in floor 9 the

2.4 GHz-Band looks like this:

(BLD_WLC05) show>client detail 34:a3:95:69:f3:80                           
Client MAC Address............................... 34:a3:95:69:f3:80
Client Username ................................. xxxxxx
AP MAC Address................................... a4:56:30:8f:8a:e0
AP Name.......................................... BLD_HK3_F9_AP3

Current Rate..................................... 54.0
Supported Rates.................................. 12.0,18.0,24.0,36.0,48.0,54.0

Radio Signal Strength Indicator............ -46 dBm
Signal to Noise Ratio...................... 47 dB

Nearby AP Statistics:

Floor 11:

      BLD_HK3_F11_AP3(slot 0)
        antenna0: 9 secs ago..................... -74 dBm
        antenna1: 9 secs ago..................... -73 dBm
      BLD_HK3_F11_AP1(slot 0)
        antenna0: 9 secs ago..................... -94 dBm
        antenna1: 9 secs ago..................... -87 dBm
      BLD_HK3_F11_AP5(slot 0)
        antenna0: 9 secs ago..................... -91 dBm
        antenna1: 9 secs ago..................... -91 dBm

Floor 10:
      BLD_HK3_F10_AP1(slot 0)
        antenna0: 9 secs ago..................... -87 dBm
        antenna1: 9 secs ago..................... -88 dBm

Floor 9:

      BLD_HK3_F9_AP1(slot 0)
        antenna0: 9 secs ago..................... -67 dBm
        antenna1: 9 secs ago..................... -70 dBm
      BLD_HK3_F9_AP1(slot 1)
        antenna0: 701 secs ago................... -85 dBm
        antenna1: 701 secs ago................... -94 dBm
      BLD_HK3_F9_AP3(slot 0)
        antenna0: 9 secs ago..................... -53 dBm

This is the one the client is connected to:
       BLD_HK3_F9_AP3(slot 1)
        antenna0: 701 secs ago................... -71 dBm
        antenna1: 701 secs ago................... -74 dBm

       BLD_HK3_F9_AP7(slot 0)
        antenna0: 9 secs ago..................... -88 dBm
        antenna1: 9 secs ago..................... -85 dBm

       BLD_HK3_F9_AP5(slot 0)
        antenna0: 9 secs ago..................... -70 dBm
        antenna1: 9 secs ago..................... -81 dBm
       BLD_HK3_F9_AP5(slot 1)
        antenna0: 702 secs ago................... -89 dBm
        antenna1: 702 secs ago................... -86 dBm

Floor 8

       BLD_HK3_F8_AP1(slot 0)
        antenna0: 9 secs ago..................... -79 dBm
        antenna1: 9 secs ago..................... -84 dBm
       BLD_HK3_F8_AP3(slot 0)
        antenna0: 9 secs ago..................... -88 dBm
        antenna1: 9 secs ago..................... -90 dBm
       BLD_HK3_F8_AP5(slot 0)
        antenna0: 9 secs ago..................... -85 dBm
        antenna1: 9 secs ago..................... -86 dBm
       BLD_HK3_F8_AP7(slot 0)
        antenna0: 702 secs ago................... -90 dBm
        antenna1: 702 secs ago................... -95 dBm

Floor 7:

       BLD_HK3_F7_AP1(slot 0)
        antenna0: 9 secs ago..................... -74 dBm
        antenna1: 9 secs ago..................... -77 dBm
       BLD_HK3_F7_AP3(slot 0)
        antenna0: 9 secs ago..................... -77 dBm
        antenna1: 9 secs ago..................... -70 dBm
       BLD_HK3_F7_AP3(slot 1)
        antenna0: 1202 secs ago.................. -88 dBm
        antenna1: 1202 secs ago.................. -88 dBm
       BLD_HK3_F7_AP5(slot 0)
        antenna0: 9 secs ago..................... -81 dBm
        antenna1: 9 secs ago..................... -86 dBm
       BLD_HK3_F7_AP5(slot 1)
        antenna0: 701 secs ago................... -87 dBm
        antenna1: 701 secs ago................... -87 dBm
       BLD_HK3_F7_AP7(slot 0)
        antenna0: 9 secs ago..................... -84 dBm
        antenna1: 9 secs ago..................... -94 dBm
     
Floor 5:

      BLD_HK3_F5_AP3(slot 0)
        antenna0: 9 secs ago..................... -84 dBm
        antenna1: 9 secs ago..................... -84 dBm
      BLD_HK3_F5_AP5(slot 0)
        antenna0: 9 secs ago..................... -96 dBm
        antenna1: 9 secs ago..................... -93 dBm

Floor 4:

      BLD_HK3_F4_AP3(slot 0)
        antenna0: 144 secs ago................... -87 dBm
        antenna1: 144 secs ago................... -92 dBm

Assisted Roaming Prediction List details:
 [0]=416  [1]=404  [2]=410  [3]=417  [4]=409  [5]=391

I have added also a picture that show the floor design for the WLAN APs that are distributed on 2 WLCs in a salt and pepper design.

The attached Word-document shows the Channel and TX-Power-assignment for three nearby floors.

What is an effective way and the right commands to check existence of Co-channel-interference ?